Nowadays, “PEG free” as a demand from both the cosmetic raw material manufacturing and the finished cosmetic product market, is clearly driving the corresponding new trend to avoid PEG, i.e. polyethylene glycol group containing ingredients. PEG materials are made from ethylene oxide, known also as EO in short, which is a petroleum derived raw material. That is already not competitive to natural based material, considering sustainability trend. Additionally, EO is a very hazardous raw material, huge caution is demanded on the manufacturing side, to minimize the risk of explosion and exposure to operational personnel. Moreover, in the field of emulsifiers and their application, performance of ethoxylated emulsifier has its weakness comparing to other emulsifiers, such as polyglycerin esters. The latter has better tolerance to electrolytes. It is also less sensitive to temperature. In optimized cases depending on the structure, the emulsification power and water resistance can be higher comparing to ethoxylated emulsifiers.
Cosmetic compositions with low viscosities have been enjoying, especially recent years, growing interest from personal care market. Such low viscosity emulsion comes with highly improved spreadability and adsorption speed. They are highly appreciated by consumers. There are many applications for stable low viscosity emulsion, for example, sprayable toner, face or body lotion, soothing lotion, sun care formulation for enhanced application properties, and so on.
The existing low viscosity emulsions mostly are oil-in-water and it is frequently sought in cosmetics due to the fact that, when applied to the skin, they give a softer, less greasy, fresher and lighter sensory than water-in-oil emulsion system, by virtue of the presence of water in the continuous outer phase.
In classical O/W emulsion systems, droplet sizes typically range between 0.5 and 20 μm. In low viscous emulsion systems, the combination of such a relatively big particle size and the density difference between internal and external phase will lead to a phase separation (tendency towards creaming of the oil droplets on top and water separation at the bottom).
The key target to obtain stable low viscous cosmetic emulsions is therefore to reduce the droplet size of cosmetic emulsions.
One option for emulsion systems with a very small droplet size are microemulsions. Different to classical emulsions, microemulsions are thermodynamically stable and have typically droplet radii of 10-40 nm which leads to clear to translucent appearance. In order to obtain such small droplets, typically high amounts of surfactants or emulsifiers are needed. A typical ratio of emulsifiers/oils for microemulsions is therefore in the range of 1/3-1/1 (B. W. Brooks, H. N. Richmond, M. Zerfa in Modern Aspects of Emulsion Science (Editor: B. P. Binks), Royal Society of Chemistry, Cambridge (1998)).
Different to microemulsions, nanoemulsions are just kinetically stable and the required production procedures are very specific. The conventional process for manufacturing nanoemulsions is the PIT method (Phase Inversion Temperature method) which utilizes the temperature-dependent hydrophilicity of ethoxylated emulsifiers [K. Shinoda, H. Saito, J. Colloid Interface Sci., 30 (1969), 258 & T. Förster, F. Schambill, W. von Rybinski; J. Disp. Sci. Technol., 13 (1992), 183]. The use of ethoxylated emulsifiers, however, is seen more and more as a disadvantage. As consumers increasingly prefer natural ingredients in cosmetics, the personal care market is extremely interested in more natural emulsions free of ethoxylated ingredients.
One option for PEG-free nanoemulsions is the so-called PIC emulsion technology which makes use of a phase inversion process at a certain water concentration upon diluting specific emulsion concentrates with water [J. Meyer, G. Polak, R. Scheuermann; Cosmetics & Toiletries, 122 (1) (2007), 61]. EP1813251 describes such nanoemulsions as long-term stable, low viscous systems with a small particle size that are in particular suitable for the use as impregnating lotions for wet wipes and sprayable emulsions.
One drawback of the systems described in EP1813251 is the fact that still a relatively high amount of emulsifier in relation to the oil is typically necessary in order to obtain good long term stability (typical emulsifier to oil ratio in the examples ˜1/3). This limitation makes it difficult for PIC emulsions to be a commercially interesting option for 0/W emulsions with an oil concentration above 10 wt. %.
CN101433500 (B) relates to a formulation of low viscosity skin lotion, the viscosities of which is ranging from 1500 mpa·s-3000 mpa·s., which is still relatively high.
US20060204468A1 described a stable PEG-free low viscosity oil-in-water emulsion. However, the emulsion is an O/W nanoemulsion which is prepared in a very specific production process via a microemulsion-like concentrate.
One of the applications of low viscosity system is to prepare spray or foam emulsion products. The lower viscosity will give better application effect on spray or pressed foam. In order to be more stable, the viscosity of spray emulsion should be increased to certain level. Then special high shearing pump will be used to make good spray or foam effect, but the cost increased undoubtedly.
So, there is an obvious and continuous need to provide stable PEG-free low viscosity oil-in-water emulsion.